Problem: Christopher ate 2 slices of pie. Daniel ate 2 slices. If Christopher ate $\dfrac{2}{5}$ of the pie, what fraction of the pie was eaten?
If 2 slices represent $\dfrac{2}{5}$ of the pie, there must have been a total of 5 slices. $\text{fraction of pie eaten} = \dfrac{\text{number of slices eaten}}{\text{number of slices total}}$ They ate ${4}$ out of $5$ slices. They ate $\dfrac{4}{5}$ of the pie.